The present invention relates to a wind turbine having a shutdown system, especially an emergency pitch drive unit. It further relates to an emergency pitch drive unit for a wind turbine, and to a method for shutting down a wind turbine.
Wind turbines need to be shutdown quickly in the event of an emergency, in order to prevent damage to the turbine. An emergency requiring a shutdown may be, for example, lightning, failure of a wind turbine component such as the generator, or failure of the network to absorb the generated power.
The shutdown operation generally includes bringing the pitch angle of the rotor blade to a feathered position, i.e. a position in which the torque exerted on the rotor by the wind is reduced. Further, the rotor may be brought to a stop, and the wind power installation pod may be rotated out of the wind.
The emergency power that is necessary to perform these tasks is usually taken from the power network. However, the emergency may be accompanied by a network failure, whence no network power is available for the shutdown. In this case, the power needs to be supplied from an emergency or backup power system. Conventionally, such an emergency power system is realized by means of accumulators, e.g. lead accumulators.
However lead accumulators have a number of disadvantages: they are relatively heavy and take up a large amount of space. Further, since lead accumulators cannot be charged and discharged an unlimited number of times, the charging and discharging properties of the lead accumulators deteriorate with time. The low trickle life of the lead accumulators is a potential safety risk, as the emergency power system is a critical part of the safety chain. Further, the low trickle life, as well as the high cost of recycling or disposing, further implies a relatively high maintenance cost. This cost increases the costs of the wind power installation and of operation thereof.
U.S. Pat. No. 6,819,086 describes an arrangement for supplying emergency power to a wind power installation. In the event of a power failure, sufficient emergency power may be supplied to reposition the rotor blades of the wind power installation and avoid damage to the overall system. This is done through the use of one or more capacitors.
Further, U.S. Pat. No. 5,907,192 describes the use of stored rotational energy for pitching blades and braking the wind turbine in the event of utility power grid failure.
However, there still is a need for an alternative emergency power supply for a wind turbine, in particular for one that is compact despite having a high energy storage capacity, environmentally friendly, easy to maintain, reliable, and/or has a fast response time.